﻿<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>鼠标移到下拉框时自动全部打开</title>
</head>
<body>

<select onmouseover="javascript:this.size=this.length" 
        onmouseout="javascript:this.size=1">
    <option>世界第一等</option>
    <option>亚洲第一山</option>
    <option>世界第一海</option>
</select>

</body>
</html>